On Wednesday 19 May 2010, Arve Hjønnevåg wrote: ... > PM: Opportunistic suspend support. > > Power management features present in the current mainline kernel are > insufficient to get maximum possible energy savings on some platforms, > such as Android. The problem is that to save maximum amount of energy > all system hardware components need to be in the lowest-power states > available for as long as reasonably possible, but at the same time the > system must always respond to certain events, regardless of the > current state of the hardware. > > The first goal can be achieved either by using device runtime PM and > cpuidle to put all hardware into low-power states, transparently from > the user space point of view, or by suspending the whole system. > However, system suspend, in its current form, does not guarantee that > the events of interest will always be responded to, since wakeup > events (events that wake the CPU from idle and the system from > suspend) that occur right after initiating suspend will not be > processed until another possibly unrelated event wakes the system up > again. > > On hardware where idle can enter the same power state as suspend, idle > combined with runtime PM can be used, but periodic wakeups increase > the average power consumption. Suspending the system also reduces the > harm caused by apps that never go idle. There also are systems where > some devices cannot be put into low-power states without suspending > the entire system (or the low-power states available to them without > suspending the entire system are substantially shallower than the > low-power states they are put into when the entire system is > suspended), so the system has to be suspended as a whole to achieve > the maximum energy savings. > > To allow Android and similar platforms to save more energy than they > currently can save using the mainline kernel, introduce a mechanism by > which the system is automatically suspended (i.e. put into a > system-wide sleep state) whenever it's not doing work that's > immediately useful to the user, called opportunistic suspend. > > For this purpose introduce the suspend blockers framework allowing the > kernel's power management subsystem to decide when it is desirable to > suspend the system (i.e. when the system is not doing anything the > user really cares about at the moment and therefore it may be > suspended). Add an API that that drivers can use to block > opportunistic suspend. This is needed to avoid losing wakeup events > that occur right after suspend is initiated. > > Add /sys/power/policy that selects the behavior of /sys/power/state. > After setting the policy to opportunistic, writes to /sys/power/state > become non-blocking requests that specify which suspend state to enter > when no suspend blockers are active. A special state, "on", stops the > process by activating the "main" suspend blocker. That looks good to me. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
